Technical Field
The present disclosure relates to the fabrication of microelectronic environmental sensors.
Description of the Related Art
Mobile computing devices such as smart phones typically include embedded electronic sensors such as, for example, magnetic field sensors (magnetometers) that can be used to determine orientation of the smart phone relative to the earth's ambient magnetic field. In addition, smart phones typically contain one or more accelerometers that sense the acceleration of gravity directed perpendicular to the earth's surface, and can detect movement of the smart phone. However, smart phones available today generally do not offer to consumers or program developers features that entail sensing, monitoring, or controlling local environmental conditions. Providing additional environmental sensors within smart phones, tablet computers, and the like, may encourage program developers to create applications that otherwise might not be possible.
Some existing products contain miniature environmental sensors. For example, electronic climate control devices (e.g., thermostats) rely on electronic sensors to trigger activation of furnaces and air conditioners for feedback control of air temperature and humidity. Electronic weather stations also rely on internal temperature sensors, barometric pressure sensors, and humidity sensors, such as, for example, those described in U.S. patent application Ser. No. 13/310,477 to LeNeel et al. Typically, these miniature environmental sensors are fabricated separately, on separate substrates (dies) from one another, or the sensors are built on one substrate and associated circuitry for signal processing and control is fabricated on a separate die (see, for example, US Patent Application Publication 2012/0171774A1 to Cherian et al.). Separate fabrication processes have been necessary because integrating more than one type of environmental sensor on the same substrate, with circuitry, poses a significant material processing challenge.
In some applications, chemical sensors have been integrated with circuitry for analyzing a chemical sample (see, for example, US Patent Application Publication 2012/0171713A1 to Cherian et al.). In other applications, chemical sensors can be built into a vehicle for delivering to the micro-sensor a chemical or biological sample for analysis, such as a razor blade (see, for example, US Patent Application Publication 2012/0167392A1 to Cherian et al.) In further applications, it has been possible to integrate temperature and humidity environmental sensors with the chemical sensors, for example, as disclosed in U.S. Patent Application Publications US 2012/0168882 to Cherian et al. However, in general, integration of multiple environmental sensors, including fluid sensors for measuring fluid pressure and flow rates, has been challenging because sensing elements for different environmental conditions typically require different, or even incompatible, materials. It is noted that the references cited above are owned by the applicants of the present patent application, and are hereby incorporated by reference in their entirety.